Means for securing a hairspring to an arbor



July 22, 1947. c Q FAWCETT I 2,424,230

MEANS FOR SECURING A HAIR SPRING TO AN ARBOR Filed Jan. 4, 1939 lnvantmv [an 11 [lPuWBEtL 31V JELQLQM Patented July 22, 1947 "MEANS FOR SECURING A *HAIRSPRIN G TO AN ARBOR Cecil C. 'Fawcett, Philadelphia, Pa.

Application January 4, 1939, Serial.No. 249,263

( Granted under the act of March 3, .1883, as amended April 30, 1928; 3700. G. 1757) Claims.

The-invention described herein maybe manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to 'a method and means for securing a hair spring to the escapement arbor in a timing mechanism, and is especially adapted for use in the timing mechanism of time delay explosive missiles.

It is well known in the art of mechanical time fuses, .as distinguished from powder train time fuzes, that the timing mechanism generally resembles a watch mechanism in principle of operation, usually differing therefrom in the manher in which it is driven and in the escapement device.

The escapement differs from that of a watch, in that it is arranged to beat at a very much higher frequency and employs a hair spring capable of withstanding and properly functioning under greater shock and usage. A satisfactory spring for use in the escapement of the mechanical fuse is one of straight length and rectangular in crosssection, or an elongated spring of similar section; however, the use of springs of these types presents problems in regard to attachment to the escapement arbor.

The general practice, heretofore, has been to insert the straight length of hair spring through a hole of circular section drilled through the arbor diametrically and to secure the spring to the arbor by inserting a circular wedge within the hole between the spring and defining surface of the hole. To obtain proper securement of the hair spring to the arbor it was necessary to so wedge that portion of the spring within the hole as to deform it into a shape generally conforming to the radius of curvature of the hole. This practice results in the spring having av medial portion of arzcuate section and end portions projecting from the hole of rectangular section, consequently upon fiexure of the spring in normal operation compound bends are developed in the spring at those points adjacent the arbor where the spring emerges from the hole in the arbor. The compound bends thus developed in the spring impose a severe strain thereon which rapidly fatigues the spring and may cause it to break rendering the fuse inoperative.

It is an object of my invention to so secure r the hair spring to the arbor as to eliminate the introduction of compound bends of the above nature in the spring when flexed.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from .a description of apreferred embodimentias shown in the accompanying drawings in which:

Fig. 1 is a side view and Fig. 2 another side viewof thearborwith thehair spring attached in accordance with my invention.

Fig. 3 is a .plan view.

Referring to the drawings the escapement arboronto which thehair spring is to be affixed is shown at l. The ends of the arbor .2, 3 are machined to provide suitable bearing surfaces, adapting the arbor to be mounted in bearings for oscillatory movement.

Intermediate its ends the arbor is formed with a recess 4 which extends from the outer surface of the arbor radially inward a distance slightly beyond the longitudinal axis of the arbor. The recess may be of any suitable configuration in cross section adapting it to the purpose of seating the hair spring. In the specific embodiment disclosed where a hair spring of rectangular cross section is used the recess is generally square at the bottom, the base of the recess being normal to its side walls and co-extensive with the arbor along a substantially diametral line.

A hair spring 5 of rectangular cross-section is seated with its medial portion in the recess 4 in such manner that its vertical transverse axis as viewed in Fig. 1 coincides with the longitudinal axis of arbor I.

For securing the hair spring 5 in recess 4 a block 5 having substantially the same configuration as the recess is inserted in the recess in engaging relation with the hair spring and welded, staked or otherwise secured at 'l to the arbor proper.

It is to be noted that by the means disclosed for securing the hair spring to the arbor that maintenance of the balance of the arbor is facilitated.

In accordance with the provisions of the patent statutes I have now particularly described the nature of this invention and the manner in which the same may be employed and I claim and desire to secure by letters patent of the United States:

1. In an escapement arbor assembly in combination, an arbor, said arbor being formed intermediate its ends to provide an inwardly extending opening which terminates adjacent the axis of the arbor, said opening having a bottom coextending with the arbor along a substantially diametral line, a hair spring medially seated in said opening and means inserted in said opening in engaging relation with the hair spring for securing the hair spring to the arbor.

2. In an escapement arbor assembly in combination, an arbor, adapted to be mounted for oscillatory movement, which comprises an intermediate portion so shaped as to provide a recess which extends radially inward and terminating adjacent the axis of the arbor, a hair spring of rectangular cross-section having its longer side co-extensive with the width of the opening, seated in the opening with its longer transverse axis coinciding with the axis of the arbor, a block of the same general configuration as the opening inserted in the opening in engaging relation to the spring and filling the opening, and means securing the block to the arbor.

3. In an escapement arbor assembly in combination, an arbor, adapted to be mounted for oscillatory movement, which comprises a portion so shaped as to provide an opening in one side extending radially inward to include and terminate adjacent the aXis of the arbor and having a bottom co-extending with the arbor along a substantially diametral line, an elongated hair spring medially seated in said opening and protruding on both sides thereof, having one of its transverse axes coinciding with the axis of the arbor, a block of the same general configuration as the opening located within said opening in engaging relation with the spring for securing the spring to the arbor and balancing the arbor and means securing the block to the arbor.

4. An escapement arbor comprising an elongated element provided with bearings at opposed ends, a portion of said element being formed as a swept-out portion with a square bottom normal toits side walls and co-extensive with the element substantially along a diametral line to provide an opening in one side extending radially inward to include and terminate adjacent the axis of the arbor and a plug fitted within said opening with its outer surface having the same general configuration as the exterior of the portion in which the opening is formed.

5. In an escapement arbor assembly in combination, an arbor adapted to be mounted for oscillating movement, said arbor being provided with a recess in one side having a bottom coextending with the arbor along a substantially diametra l line, a hair spring medially seated in said recess and protruding on both sides thereof, and means of the same general configuration as the recess inserted therein in engaging relation with the hair spring for securing the latter to the arbor.

CECIL C. FAWCETT.

REFERENCES CITED UNITED STATES PATENTS Name Date Bold Oct. 13, 1925 Number 

